1. Field of the Invention
The present invention relates to a gripping device provided at an end of a working arm of a working machine such as a hydraulic excavator, and used for gripping a processing object for, for example, tearing down a building or breaking up and separating industrial waste; and to a working machine including the gripping device.
2. Description of the Related Art
Hitherto, a gripping device discussed in Japanese Patent No. 2691795 (hereunder referred to as “Patent Document 1”) is known as a gripping device provided at an end of a working arm of a working machine. The gripping device includes a frame bracket, a pair of arm links, an arm cylinder, and link connecting members for gripping. The frame bracket is mounted to the end of the working arm. The pair of arm links are provided at the frame bracket so as to be openable and closable with respect to the frame bracket. The arm cylinder opens and closes the arm links. Each link connecting member is provided at one end of its corresponding arm link. More specifically, each link connecting member for gripping includes a plurality of gripping links and pins that connect the gripping links that are adjacent thereto. By applying tension to or removing tension from a tension member, such as a wire, provided between the gripping link at the outermost end and a rotating frame, the link connecting members can be bent along a periphery of a grip object.
A gripping device discussed in Japanese Unexamined Utility Model Registration Application Publication No. 57-80554 (hereunder referred to as “Patent Document 2”) is known as a another gripping device. The gripping device includes a supporting bracket, a pair of gripping arms, and a cylinder device. The supporting bracket is mounted to the end of the working arm. The pair of gripping arms are rotatably mounted to the supporting bracket. The cylinder device rotates the gripping arms. The cylinder device causes the gripping arms to perform gripping operations by rotating both of the gripping arms in opposite directions.
The gripping device may be required to provide a large gripping force. In particular, for the purpose of breaking a strong work object, a very large driving power is required, thereby making it necessary to include a cylinder device providing a large output as the aforementioned cylinder device.
However, a large gripping device, such as that mentioned above, used for the purpose of performing, for example, a powerful breaking operation can seldom grip a relatively small work object without breaking the small work object. In such a powerful gripping device, the gripping force varies greatly even by a slight operation performed by an operator, thereby making it difficult for the operator to finely adjust the gripping force by operating the powerful gripping device.
The gripping device according to Patent Document 1 can grip a grip object using the pair of link connecting members that are bent along the periphery of the grip object. Therefore, the gripping device can grip the grip object without breaking the grip object. However, since the grip object is gripped by the link connecting members that can be bent along the periphery of such a gripping device, even if the arm cylinder that opens and closes the gripping links is one providing a large output, the link connecting members are deformed, thereby preventing a sufficient driving force from being transmitted to the grip object.
According to Patent Document 2, the gripping device includes an auxiliary gripping member removably mounted to an end of each gripping arm; a portion of each auxiliary gripping member that contacts a processing object is formed of an elastic material such as rubber; and each auxiliary gripping member is mounted only when gripping a relatively small processing object. However, even if such auxiliary gripping members are mounted, the driving force of the cylinder device is transmitted to the processing object as it is, thereby making it difficult to perform fine adjustments of the gripping force. In addition, there is a considerable limit as to how thick the elastic material can be made, as a result of which it is actually impossible to effectively accommodate a sudden increase in the gripping force by elastic deformation of the elastic material alone. Consequently, when the output of the hydraulic cylinder device is suddenly increased by gripping a small processing object, breakage of the processing object caused by the gripping is rarely prevented from occurring.